What is the error message "Cannot modify header information - headers already sent" in PHP indicating?

The error message "Cannot modify header information - headers already sent" in PHP indicates that there was an attempt to send HTTP headers after some content has already been sent to the browser. This commonly occurs when there is whitespace or other output before the `header()` function is called. To solve this issue, make sure that there is no output (such as HTML, whitespace, or echo/print statements) before calling the `header()` function. 

<?php
ob_start(); // Start output buffering

// Your PHP code here

ob_end_clean(); // Clean the output buffer without sending any data

header("Location: newpage.php"); // Redirect to a new page
exit();
?>

Keywords

PHP headers output buffering ob_start ob_end_clean

Related Questions